This invention relates to the manufacture of corrugated rubber tubing of relatively large diameter and wall thickness and, more particularly, to power driven apparatus for fabricating such tubing.
More particularly, the invention relates to an apparatus for making such corrugated tubing from sleeves of relatively large diameter and wall thickness such that the forces necessary for forming embryonic corrugations in the uncured rubber prior to curing are too great to be obtained by human strength as required in accordance with the teachings of U.S. Pat. Nos. 3,168,604 and 3,304,581.
As disclosed in U.S. Pat. Nos. 3,168,604; 3,304,581 and 3,669,586, corrugated tubing with annular or helical corrugations may be made with forming devices including axially spaced annular discs or helical convolutions that are employed with forming mandrels to produce embryonic corrugations in uncured rubber sleeves. Each time a tube is formed, the forming member is placed over the forming mandrel, on which the sleeve has been positioned, and the sleeve is radially expanded so that it bulges into the spaces between the discs or helical convolutions, forming creases between the bulges. According to the aforesaid patents, the forming member and sleeve are then collapsed axially so that the sleeve is axially compressed, concertina fashion. The creases together with adjacent bulges provide embryonic corrugations. Then the forming member is axially extended together with the sleeve after which the sleeve is removed from the forming mandrel and placed on a cylindrical curing mandrel where it is axially foreshortened, concertina fashion, into corrugated form with the desired spacing between adjacent annular or helical corrugations.
For some uses, it is desirable to provide flexible corrugated tubing of relatively large diameter and wall thickness. For example, such tubing is particularly useful for exhausting noxious gases from vehicle engines at garages where automotive service is performed. Tubing for this purpose should have an interior passage diameter of from 21/2 to 6 inches or more. Because of the high temperature of the exhaust gases which pass through the tubing, it is necessary that certain special vulcanizable compounds be used so that the resulting product has a high thermal resistance.
Because of the relatively large wall thickness of the extruded sleeves used to make the tubing, the manual process formerly used (for example, the process of U.S. Pat. No. 3,168,604) may not be employed because the forces required to perform the step of axially collapsing the forming member and sleeve to compress the sleeve concertina fashion and form the embryonic corrugations, are too great to be generated with human strength. The largest corrugated tubing that it has been possible to make under the aforesaid manual process has been 11 ft. long with an inner diameter of 2 inches and a wall thickness of 3/32 inches.
While it is possible to make large diameter tubing with helical corrugations using the cording method disclosed in U.S. Pat. No. 2,832,096, this method cannot be used to achieve high production rates. Furthermore, the length of corrugated tubes that can be made using the cording method is limited to about 12 ft. Forming mandrels longer than 12 ft. bend too easily and a whipping action occurs that disrupts the cording process. Also, where high temperature resistant compounds are used the cording method is impractical because of problems encountered in curing the sleeve with the cord wrapped thereon.
The method and apparatus of the present invention make possible the manufacture of large diameter tubing (e.g., with an inner diameter of between 21/2to 6 inches or more) using the method of U.S. Pat. No. 3,168,604, by providing a novel means for generating the necessary forces to compress the sleeve of uncured vulcanizable material concertina fashion to form embryonic corrugations. Corrugated tubing lengths up to 23 ft. or more may be produced in this manner. The invention also affords other features and advantages heretofore and not obtainable.